1. Field of the Invention
The present invention relates to a process for the preparation of methyl tertiary butyl ether (MTBE) or ethyl tertiary butyl ether (ETBE) wherein tertiary butyl alcohol (TBA) is reacted with methanol or ethanol and an effluent is formed which contains the water of reaction and at least 1 mol of methanol or ethanol for each 2 mols of MTBE or ETBE, the effluent is distilled to separate a mixture of ether and methanol or ethanol overhead from a bottoms which comprises the water of etherification, unreacted TBA and methanol or ethanol, and the overhead, preferably after distillation to reduce the methanol or ethanol content, is reacted with isobutylene to convert the lower alcohol contained therein to additional quantities of alkyl tertiary butyl ether.
2. Description of the Prior Art
MTBE and ETBE are important chemicals of commerce which have great utility, for example, as gasoline blending agents.
In the oxirane propylene oxide/TBA process there are produced both propylene oxide and tertiary butyl alcohol in exceedingly large quantities. It is advantageous to form MTBE and ETBE using the TBA formed in the above process.
Methods are known for the formation of MTBE and ETBE by reaction of the lower alcohol with isobutylene as well as by reaction of the alcohol with TBA.
A problem with the production of MTBE and ETBE by reaction of the lower alcohol and TBA is that water is a co-product of the reaction which is very difficult to separate from product ether since the two form an azeotrope which is expensive to break.
A problem with the production of MTBE or ETBE by first dehydrating TBA to isobutylene which is then reacted with the lower alcohol is that for liquid phase dehydrations, water is the heavy component which builds up, killing the reaction. Vapor phase dehydration is very costly in terms of capital and operating expense. The reaction of isobutylene with methanol or ethanol is highly exothermic, requiring large recirculation to remove heat of reaction, and the formation of the ether-lower alcohol azeotropes causes large recycle of ether to remove excess alcohol.
U.S. Pat. No. 4,918,244 shows the preparation of MTBE by reaction of TBA and methanol. The patent shows the distillation overhead of a MTBE and methanol mixture which is separated by gasoline and water extraction.
U.S. Pat. No. 5,099,072 shows the reaction of TBA and methanol to form MTBE.
U.S. Pat. No. 4,925,989 describes a process for preparing MTBE by feeding TBA, isobutylene and methanol to a combination reactor distillation tower.
U.S. Pat. No. 4,144,138 shows MTBE recovery from a reaction effluent containing MTBE, TBA, methanol and water by azeotropic distillation and extraction techniques.
U.S. Pat. No. 4,822,921 shows MTBE production by reaction of TBA and methanol.
European Publication 0 502 265 shows an integrated process for the production of MTBE involving, in part, reaction of isobutylene with methanol.
European Publication 0 502 651 shows MTBE production by reaction of TBA and methanol.